WASHINGTON -- Shining a constitutional spotlight on the rapidly growing private prison industry, the United States Supreme Court today ruled that guards employed at such prisons are not shielded from prisoner lawsuits alleging general abuse and mistreatment.

The 5 to 4 decision, written by Justice Stephen Breyer marks the first ruling by the nation's high court on whether privately employed prison guards can invoke immunity from lawsuits for all but the most egregious offenses.

The American Civil Liberties Union, which filed a friend-of-the-court-brief in the case, praised the ruling as a sensible check on private companies whose bottom line may sometimes compromise prisoner safety.

"Private prisons exist primarily to make a profit, not to serve the public," said Steven R. Shapiro, the ACLU's National Legal Director. "This decision will help ensure that a company's profit margin does not cut into a prisoner's constitutional right to be free from cruel and unusual punishment."

The case was brought on behalf of Ronnie Lee McKnight, an inmate at the South Central Corrections Center, a privately run prison in Clinton, Tenn. operated by the Corrections Corporation of America, one of the largest firms in the field.

McKnight, who weighs approximately 300 pounds and is in poor health, charged that he suffered injuries caused by two prison guards who handcuffed and shackled him too tightly during transport. Despite pleas that the restraints were cutting circulation to his limbs, causing him intense pain and swelling, the guards refused any assistance. The incident landed him in the hospital.

Attorneys for the company had argued that their employees should be protected from lawsuits under a doctrine known as qualified immunity that shields state officials, including guards at public prisons, from liability, expect for the most serious abuses.

In rejecting that line today, the Supreme Court affirmed the rulings by the lower federal courts that the rationale behind qualified immunity -- minimizing lawsuits that might undermine the public interest in government efficiency -- does not apply to private companies which are more concerned with

shareholders' interests than the public's.

The last decade has seen a dramatic growth in the private prison industry. There are currently more than 20 such companies nationwide, earning more than $250 million a year, and managing some 90 prisons that house approximately 50,000 inmates. But that explosive rise, the ACLU says, has occurred with a minimum of oversight by the federal courts.

"Recent studies have suggested that privately run prisons may not be as cost-effective for the public and lucrative for its investors as once thought," Shapiro said. "At a time when these companies are keeping an even closer eye on the profit line, the Supreme Court has made sure they also watch out for their guards' excesses."

Founded in 1920, the ACLU is a nationwide, non-partisan organization dedicated to defending and preserving the Bill of Rights for all individuals through litigation, legislation and public education. With the exception of the Justice Department, the ACLU is involved in more cases before the Supreme Court than any other individual or organization.